(i) Field of the Invention
The present invention relates to a detecting apparatus for monitoring abnormality during the step of producing a folded fiberboard box in a fiberboard box making machine and more particularly to an apparatus for detecting abnormality relative to quality of a folded box at the production stage where a sheet of corrugated fiberboard is folded while both the folded ends are located opposite to one another with a certain gap interposed therebetween.
(ii) Prior Art Statement
The conventional box making machine is constructed so as to make a fiberboard box by folding a square sheet of smooth corrugated fiberboard which is cut to predetermined dimensions by means of a corrugator which serves as a preprocessing line. Specifically, it has many functions which comprise cutting of unnecessary corners, scribing of contour lines, printing, folding, gluing and preforming prior to assembling. Due to fact that the conventional box making machine has various processing functions as mentioned above, each of processing functions is achieved by operating a specially designed unit and a series of fiberboards are successively conveyed while a certain distance is maintained between the adjacent fiberboards at every time when a certain function is completed in a series of processing units.
FIG. 6 is a fragmental schematic side view of the conventional box making machine. In the drawing reference numeral 1 designates a folded fiberboard box which is made of a sheet of smooth corrugated fiberboard by folding the latter in a folding unit. After completion of making of the folded box 1 the latter is discharged from the folding unit by rotating a pair of guide rolls 3 and thereafter thus discharged boxes 1 are piled one above another in the space as defined between both retaining plates 4 in the layered structure. After a number of folded boxes 1a are piled one above another in the above-described manner, the lowermost folded box 1b is conveyed away from the layered structure to reach the next processing unit 6 such as a counter unit or the like and this step of operation is repeated successively.
However, it is found with respect to the conventional box making machine that abnormality relative to quality as corrugated fiberboard box tends to take place in the area located in vicinity of the above-mentioned units in the following manner. FIG. 7 shows a folded box 1b as seen in the direction as identified by an arrow mark VII in FIG. 6, wherein FIG. 7(A) shows a normally folded box by way of perspective view and FIG. 7 (B) shows a corrugated fiberboard box which is incorrectly folded in the so-called fishtail shape with some projection from the folded part recognized. In the case as shown in FIG. 7(B) the gap in the junction area has a dimension of G.sub.1 at the upper part but it has a different dimension of G.sub.2 at the lower part of the folded box as seen in the drawing.
This abnormality in shape takes place when folding lines, that is, working lines are scribed incorrectly. In some case it takes place because of incorrect relative displacement of the folded part which is caused under the influence of shearing force which is developed during conveyance of the folded box 1b while the latter is depressed by many other folded boxed 1a. Once such an incorrectly folded box is produced, this leads to reduction of commercial value thereof. In addition it is necessary to keep some inspectors in a stacker section in order to inspect quality of all products to remove incorrectly folded boxes.